The specific aims of this proposal are to obtain high-resolution structures of the cGMP binding domains of cGMP-dependent protein kinases (PKGs) and to use the structural information to design activators specific for PKG. As key receptors for cGMP, PKGs mediate most effects of cGMP elevating drugs such as nitric oxide releasing agents for the treatment of many hypertensive diseases and phosphodiesterase inhibitors for the treatment of erectile dysfunction. While PKGs are proven therapeutic targets for treating hypertensive diseases such as arterial and pulmonary hypertension, heart failure and erectile dysfunction, developing specific activators has been difficult mainly due to a lack of available structural information. In pursuit of structural information that may facilitate the development of specific activators of PKG, our group recently determined crystal structures of a fragment of the regulatory domain of human PKG I that specifically binds cGMP and activates the catalytic activity. To our knowledge, these data represent the first crystal structures known for this important domain. Our preliminary structural analysis combined with computational docking models suggests that there are many druggable sites near the cGMP binding pocket. Some docking models also suggest that derivatizing the 6- and 8-positions of the purine ring of cGMP may provide additional contacts with the protein without disrupting the existing contacts. My long-term goals are to understand the activation mechanism of PKG mediated by cGMP and to develop specific activators of PKG that can be used for treating hypertensive diseases. To achieve these goals, my plans are to determine crystals structures of the regulatory domain of PKG I (Aim #1), and to design/synthesize/test cGMP analogs that sustain the activity of PKG (Aim #2).